Perhaps you should try some spelling variations:
su sach » so sach, vu sach
hieu va » lieu va, hieu qua
va dang » van dang, va nang, va lang
duc van » duc tan, duc manh, duc phan
cua tre » cua te, cuu tre, cua triet
y nang » ky nang, ly nang, v nang
vi cua » vai cua, di cua
o hoi » co hoi, o hai, o hoa
o hoc » co hoc, mo hoc, so hoc

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: su sach y nang ((o hoi) OR (o hoc)). hieu va dang ((duc van) or (duc va)) hanh vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach y nang ((o hoi) OR (o hoc)). hieu va dang ((duc van) OR (duc va)) hanh vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach y nang ((o hoi) OR (o hoc)). hieu va dang ((duc van) or (duc va)) hanh vi cua tre".
• Adding a wildcard symbol may retrieve word variants: su sach y nang ((o hoi) OR (o hoc)). hieu va dang ((duc van) or (duc va)) hanh vi cua tre*.